There are increasing needs for inspections and analyses of semiconductor devices advancing in miniaturization. Among them, an essential technique for a failure analysis for identifying a cause of defect is to directly observe a defect inside a device. For such observation, it is necessary to perform accurate microfabrication of the observation target position of the device. Focused ion beam (hereinafter, FIB) processing systems have been heretofore used as apparatuses for performing the accurate microfabrication. The FIB systems are each capable of accurately processing the target position by performing electrostatic deflection scanning with an ion beam focused to a submicron size and irradiating the sample with the ion beam. Thus, the FIBs are used in formation of cross sections for analyses, fabrication of samples for analyses, and the like.
Transmission electron microscopes (hereinafter, TEM), scanning transmission electron microscopes (hereinafter, STEM), and the like are used in high-resolution observations. In order to observe a sample by using the TEM or STEM, the sample needs to be processed to have a thickness small enough for an electron beam to pass through the sample, e.g., approximately 100 nm. Because of the recent advancement in miniaturization of the devices, the film thickness management of thin film samples becomes important for sample fabrication by which the observation target position should be accurately positioned within each thin film sample.
Examples of a technique to monitor the thickness of a thin film include the techniques respectively disclosed in Japanese Patent No. 3223431 (Patent Document 1) and Japanese Patent 3221797 (Patent Document 2). In these techniques, the thin film to be processed by an FIB is irradiated with an electron beam and a transmission electron volume of the electron beam is detected to monitor the film thickness of the thin film to be processed. Furthermore, Japanese Patent No. 3119959 (Patent Document 3) discloses that a thin film to be processed by an FIB is irradiated with an electron beam, the irradiation intensity and transmission intensity of the electron beam are detected, and the film thickness is monitored by using the intensity ratio therebetween. Moreover, Japanese Patent Application Publication No. 2006-127850 (Patent Document 4) discloses that a thin film to be processed by an FIB is irradiated with an electron beam, a signal luminance change is detected by a transmission electron detector and a scattered electron detector, and whether the film thickness is a desired one is determined based on the signal luminance change.